A switching system or a method for checking the switching region is used both in the private sector and also in the industrial sector. The switching system has the function of detecting when a signal emitter enters into, and remains within, an effective region of the switching system and thereupon for example reporting the event or triggering a switch-on, switch-off or protective switching operation. The triggering occurs for the most part in the situation when the carrier of the signal emitter is detected within the effective region, or is detected or no longer detected for a certain period of time within this effective region. As a general rule, the carrier constitutes a mobile unit which is to be made identifiable or trackable for a sensor by the signal emitter.
For example, the safety door (shut-off barrier) of a press can be equipped with such a switching system such that when the door which carries a signal emitter is opened, this ensures that the press is unable to generate any pressure. The switching system acting in touch-free fashion consequently prevents the activation of the press while people or objects are located in the danger area.
As a general rule a touch-free switching system is implemented as a position switch or safety switch which consists of at least two independently movable parts, the sensor and the signal emitter. The sensor communicates with the signal emitter, for example by way of magnetic or electromagnetic alternating fields. For example, in response to a request from the sensor or in the presence of a magnetic or electromagnetic alternating field the signal emitter sends data which as a general rule contains a serial number as an identification number and a check sum. In principle, sending any code is sufficient, however in practice the use of a serial number, a check sum and also a freely programmable portion within the code has become accepted.
For example, the serial number can be used in order to identify the signal emitter and to possibly trigger signal emitter-dependent switching operations. The check sum on the other hand has the function of guaranteeing error-free transmission. As already described by way of example, the position switch or safety switch is provided for the purpose of releasing the safety-relevant effective region only in the situation when the signal emitter is situated within a defined switching region relative to the sensor.
Effective regions of the position switch or safety switch can in practice have extremely complicated, three-dimensional shapes. The shape of the effective region depends on the immediate surrounding area, and also on transmission-related parameters, such as the antenna for example.
As a general rule, current position switches or safety switches acting in touch-free fashion have three switching regions. Firstly, in the immediate surrounding area of the sensor itself is situated the switch-on region, which is surrounded by the so-called hysteresis region. The hysteresis region in turn is surrounded by the switch-off region. The reason for the need to distinguish between the three switching regions lies in a continuous decline in the transmission power as the distance from the sensor increases. Switching regions delimited from one another can thus be specified having regard to the tolerances.
In the case of the technologies employed up to now, the switching regions are predetermined by numerous system parameters. It should be noted that the switch-on region is separated from the switch-off region by the hysteresis region. No switching can take place within this region because no reliable detection is possible. A signal emitter or its carrier must therefore, for example, move out of the switch-off region through the hysteresis region and into the switch-on region before a switch-on can be triggered.
A position monitoring facility is known from EP 1 638 206 A2 for determining the position of a first part compared with a second part. The monitoring is accomplished by using a transceiver mounted on the first part and a transponder mounted on the second part, whereby the position limit distance can be changed by means of a movable screen.
A disadvantage resides in the fact that it is not possible to identify a plurality of switch-on regions and/or switch-off regions. Hitherto only two states of the system are possible, for example a switch-on state and a switch-off state. The user is required to tolerate the predefined switch-on and switch-off regions which were determined by the system parameters and tolerances of the equipment and to select the appropriate switching system or systems for his application. This is a very elaborate and cost-intensive procedure.